This invention relates to an apparatus for measuring a lateral shift of running magnetic tape caused by lateral movement of the magnetic tape which occurs while the magnetic tape is running.
The magnetic tape that has commonly be used as data storage for a computer in recent years has an increasing recording density to enlarge a storage capacity thereof. Therefore, data tracks on which data are written and recorded are designed to be very narrow; for example, some magnetic tape has a track width of approximately 10-20 μm. In such narrow-track magnetic tape, lateral movement (side-to-side movement) of the magnetic tape which is likely to occur while the magnetic tape is running would affect the reliability of a magnetic tape drive that reads/writes data from/onto the magnetic tape, and thus should preferably be minimized. Accordingly, the lateral movement of magnetic tape as described above need be measured on several occasions in the course of development of a magnetic tape cartridge or a magnetic tape drive.
When lateral movement of magnetic tape is measured, hitherto known techniques, as disclosed in JP 2000-339792 A, used to measure a position of a side edge of the magnetic tape which is running in the drive, utilizing a photo interrupter or the like.
However, the change in position of the side edge of the magnetic tape results from a combination of lateral movement of the magnetic tape due to uneven distribution of stress or the like and variation of the width of the magnetic tape due to widthwise dimensional errors. To be more specific, the width of the magnetic tape is not completely maintained uniform along the length, and the position of the side edge of the magnetic tape changes due to errors in shape or size as described above, as well as an actual shift in position. Consequently, the methods for measuring lateral movement according to the aforementioned conventional techniques cannot measure the true movement only due to a lateral shift in position of the running magnetic tape.
The present invention has been proposed to eliminate the above-described disadvantages in the conventional techniques; therefore, it is an exemplified object of the present invention to provide an apparatus for measuring a lateral shift of running magnetic tape caused by lateral movement of the magnetic tape which occurs while the magnetic tape is running.